iN NEED of POT

[rcafan]

I need a field neutralization pot for the CT100. It is
A 30 ohm wire wound ,2watt, tapped at 15 ohms..
Did anyone create a solution for this?

Thanks in advance

[Steve McVoy]

Try this:

[miniman82]

Same thing I just replaced, John Folsom sent me one. On the back, it has some numbers:

1990255
625-8024

It's a 50 ohm job, close enough to the original. Can't find any info on it.

[Electronic M]

There is a joke some where in that thread title......But I don't feel motivated to fish for it presently.

I like Steve's solution it illustrates just how handy ohm's law is.

[miniman82]

It's handy if you're not interested in the originality of the chassis, though I suppose if you can't get a 30 ohm one....

[bob91343]

I need two pots - 100 Ohms and 50 Ohms, linear, 2 Watts.

[Pete Deksnis]

Things they say happen in threes. so it is no surprise that three days ago the last Field Neutralization pot I have went belly up. The same one Nick and RCAfan need. I thought I had a spare in an unrestored CTC2 chassis that had been little used throughout its long-ago active life. But this pot too was open. Like the one in my operational chassis, the open is at one end of the wire-wound resistance element. So, I came up with a kluge circuit shown that uses both bad pots and a switch to get the chassis running again.

How's the field neutralization control work? Operationally, rotating the wiper to either side of center changes the direction (and amount) of current flow through the field neutralization coil (which rings the 15GP22 faceplate). Now, a switch is used to change direction of current flow, and the associated pot is then adjusted for appropriate current through the coil.

Another possibility is repair. The 'fried' pot lost about the frst five turns of wire at one end. Picture attached. Perhaps if I'm lucky, I can lay a slurry of solder across the charred turns. But it's probably not doable. (Has anyone fixed a WW pot?). When I checked the other pot, it was NOT burned out -- it seemed to have failed from a design flaw. Picture attached.

The pots have twin wiper assemblies; you can see the two arcs they made as they scraped the turns of wire. There are two places where the resistance wire is compromised. One is a single break about twenty turns from the end. The other a group of breaks in the first ten or so turns of wire. I believe the stress from the wiper was much greater near the end of its travel and easily broke the wires. Close inspection with a magnifier suggests much more abrasive wear from the wiper very near the end of its rotation. If I'm correct, it might explain why a seemingly low-electrical-stress WW pot appears to have a high failure rate.

Pete

[bob91343]

In my case, one of the pots has a broken wiper. The other is frozen in position, which the first one was too until I broke the wiper. So I don't want to attempt repairing the other frozen pot else I won't have a working unit until I find a replacement. I used resistors as a temporary fix for the first broken pot.

[Zenith6S321]

I was able to repair the wirewound bias pot on a Hickok 539B tube tester using the conductive paint from an automotive defroster repair kit. In my case I was able to remove the WW element from the pot case and flip it over so that the wiper now rubs on the unused edge. I used an ohm meter to find the three open sections and carefully used the paint to bridge the gap on the edge where the wiper originally contacted the wire. That was a year ago and the tester is still working fine.

[Zenith6S321]

Here is a link to what I used: http://www.amazon.com/Permatex-15067.../dp/B000HBI9YQ

[John Folsom]

bob91343, check surplus sales of nebraska for the pots you need (assuming they are NOT center tapped)

http://www.surplussales.com/Potentio...PotsIndex.html

[Phil Nelson]

Originally Posted by Pete Deksnis

Perhaps if I'm lucky, I can lay a slurry of solder across the charred turns. But it's probably not doable. (Has anyone fixed a WW pot?).

How about silver-filled epoxy (the stuff in the top of this photo)?



Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

[Tim]

When I restored my set, I discovered that the pot had opened and I could actually see where it had burned. I was able to scrape insulation off of the adjacent wires and put a drop of solder on it to repair it. The drop was a little bigger than I would have liked but it has worked well and held up with no further problems.

[bob91343]

John, Nebraska doesn't have 2 W pots in the resistance needed. A little pricy anyway, I think, especially factoring in shipping. I'd like to get them locally.

I will try All Electronics next time I am out that way. I haven't been to Apex lately but they might have something.

[rcafan]

How about this arrangement?